Bioenergy to save the world
Transcription
Bioenergy to save the world
Novel Energy Plants Subject Area 5.2 OpenChoice Area 5.2 • GMOs, Bio-Products, Bio-Processing Discussion Article Bioenergy to Save the World Producing novel energy plants for growth on abandoned land* Peter Schröder1*, Rolf Herzig2, Bojin Bojinov3, Ann Ruttens4, Erika Nehnevajova2, Stamatis Stamatiadis5, Abdul Memon6, Andon Vassilev7, Mario Caviezel8 and Jaco Vangronsveld4 1 Helmholtz-Zentrum München, German Research Center for Environmental Health, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany Quartiergasse 12, 3013 Bern, Switzerland 3 Dept. Plant Plant Genetics, Agricultural University of Plovdiv, Mendeleev Str., 4000 Plovdiv, Bulgaria 4 Universiteit Hasselt, Campus Diepenbeek, Environmental Biology, Agoralaan, Building D, 3590 Diepenbeek, Belgium 5 Soil Ecology and Biotechnology Laboratory, GAIA Environmental Research and Education Center, Kifissia, Greece 6 TUBITAK Research Institute for Genetic Engineering and Biotechnology, Gebze, Turkey 7 Dept. Plant Physiolgy and Biochemistry, Agricultural University of Plovdiv, Mendeleev Str., 4000 Plovdiv, Bulgaria 8 CTU Konzepte Technik und Umwelt, Buerglistr. 29, 8400 Winterthur, Switzerland 2 Phytotech-Foundation, * Corresponding author: Prof. Dr. Peter Schröder, Helmholtz-Zentrum-München, German Research Center for Environmental Health, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany ([email protected]) DOI: http://dx.doi.org/10.1065/espr2008.03.481 Please cite this paper as: Schröder P, Herzig R, Bojinov B, Ruttens A, Nehnevajova E, Stamatiadis S, Memon A, Vassilev A, Caviezel M, Vangronsveld J (2008): Bioenergy to Save the World. Producing novel energy plants for growth on abandoned land. Env Sci Pollut Res 15 (3) 196–204 Abstract Background and Aim. Following to the 2006 climate summit, the European Union formally set the goal of limiting global warming to 2 degrees Celsius. But even today, climate change is already affecting people and ecosystems. Examples are melting glaciers and polar ice, reports about thawing permafrost areas, dying coral reefs, rising sea levels, changing ecosystems and fatal heat periods. Within the last 150 years, CO2 levels rose from 280 ppm to currently over 400 ppm. If we continue on our present course, CO2 equivalent levels could approach 600 ppm by 2035. However, if CO2 levels are not stabilized at the 450−550 ppm level, the consequences could be quite severe. Hence, if we do not act now, the opportunity to stabilise at even 550 ppm is likely to slip away. Long-term stabilisation will require that CO2 emissions ultimately be reduced to more than 80% below current levels. This will require major changes in how we operate. Results. Reducing greenhouse gases from burning fossil fuels seems to be the most promising approach to counterbalance the dramatic climate changes we would face in the near future. It is clear since the Kyoto protocol that the availability of fossil carbon resources will not match our future requirements. Furthermore, the distribution of fossil carbon sources around the globe makes them an even less reliable source in the future. We propose to screen crop and non-crop species for high biomass production and good survival on marginal soils as well as to produce mutants from the same species by chemical mutagenesis or related methods. These plants, when grown in adequate crop rotation, will provide local farming communities with biomass for the fermentation in decentralized biogas reactors, and the resulting nitrogen rich manure can be distributed on the fields to improve the soil. Discussion. Such an approach will open new economic perspectives to small farmers, and provide a clever way to self sufficient and sustainable rural development. Together with the present economic reality, where energy and raw material prices have drastically increased over the last decade, they necessitate the development and the establishment of alternative concepts. Conclusions. Biotechnology is available to apply fast breeding to promising energy plant species. It is important that our valuable arable land is preserved for agriculture. The opportunity to switch from low-income agriculture to biogas production may convince small farmers to adhere to their business and by that preserve the identity of rural communities. Perspectives. Overall, biogas is a promising alternative for the future, because its resource base is widely available, and single farms or small local cooperatives might start biogas plant operation. Keywords: Agriculture; bioenergy; biogas; biomass; CO2 lev- els; energy plants; fossil fuels; greenhouse gases; Kyoto protocol Introduction The World Energy Outlook 2006 (www.IEA.org) specifies that the world will have to face two energy-related threats: the first of not having adequate and secure supplies of energy at affordable prices and the second of environmental harm caused by consuming too much of it. Hence, the G8leaders postulated the need to decrease fossil-energy demand in favour of geographic fuel-supply diversity. Mitigating climate-destabilising emissions is more urgent than ever. They * This work was stimulated by discussions within COST Actions 837 and 859. 196 Env Sci Pollut Res 15 (3) 196 – 204 (2008) © Springer-Verlag 2008 Subject Area 5.2 called on the IEA to "advise on alternative energy scenarios and strategies aimed at a clean, clever and competitive energy future" (IEA 2006). Although the outlook paints a dark picture of the development until 2030, it makes a clear statement that biofuels and renewables could make up to 12% of the global energy budget if the right measures be taken. But the report does also state clearly that increasing food demand, which competes with biofuels for existing arable and pasture land, will constrain the potential for biofuel production. Hence, it is clear that sustainable and efficient biomass production must not proceed on valuable arable land but on so far neglected and set aside plots. This means that solutions have to be proposed for soils that have been abandoned, e.g. because they may be degraded, polluted or non-exploited, relatively poor soils. Similarly, the EREC (European Renewable Energy Council) concludes that adopting the targets for the share of bioenergy will be the basis for the continuation of a sustainable EU energy policy, as well as a precondition for establishing a sustainable, competitive and secure energy mix for the future (EREC 2006). In 2003, the European Commission initiated the European Technology Platform 'Plants for the Future' as a stakeholder forum on plant genomics and biotechnology. This platform is supported by the European Commission and major public and private stakeholders. It is coordinated by EPSO (www.epsoweb.org/catalog/tp/), whose high-ranking plant physiologists sketched their opinion about future developments in food and energy crops. They claim that we presently do not fully exploit the potential in plants, and that the world can be supplied with sufficient nutrients and energy when biotechnology of plants is boosted (http://www. europabio.org/relatedinfo/Plantgenbrochure.pdf). It is necessary to note that generation of genetically modified plants is just one biotechnology, the use of which is controversially discussed with view to safety of global food and feed supply (Young 2003, 2004, Gaugitsch 2004). Providing the world with bioenergy using more conventional ways of classical breeding is another option which has been postulated even earlier. Ambitious papers on the production of plant-derived energy from green and animal manure have been published as early as in the 1980s (Drake 1983, Long 1984). Progress is likely to result from a combination of plant breeding, plant and microbial metabolic engineering, and chemical engineering, hence delivering fuel with a much smaller ecological footprint (Abraham 2007). European border countries and countries of the Mediterranean will encounter particular problems when trying to adopt bio-energy plants to fight climate change, because their production systems are concentrated in areas of high fertility and water availability. Hence, substituting crops for energy plants will lead to shortage in food production and soil resources. 1 Bioenergy Options The use of bio-based strategies to fulfil our energy demands is most promising. Recent literature has already identified several crops, amongst them maize, wheat, potatoes, rapeseed and others, that can be produced on European arable land to substitute fossil fuels and make the European energy Env Sci Pollut Res 15 (3) 2008 Novel Energy Plants market more independent. Bio-ethanol production, biodiesel (i.e. rapeseed oil methyl ester) and biogas (i.e. methane and aliphatic gases) from plant sources are in the focus of interest (Young 2003). In fact, production of energy crops is already ongoing, and technologies for bio-fuel production are established in richer countries. However, explicit accounting for CO2 at each stage of the production process is essential to decide for the most environment-friendly alternative (Rabl et al. 2007). Biogas produced from animal manure, wastes and fresh biomass ranks amongst the most sustainable energy forms, especially because of its potential production in small, decentralized units that require no big transport infrastructure. Hence, it may be an alternative of incredible potential for rural areas of low standards and with lacking infrastructures where it will deliver heat, gas to be stored and electrical energy to small farms and communities. As reviewed by Markard et al. (2002), biogas from agriculture has many ecological advantages. Being renewable, it may substitute fossil energy carriers, and will also reduce emissions of methane gas from 'natural' (i.e. uncontrolled) decomposition processes of organic matter. Hence, biogas production can mitigate greenhouse gas emissions. Biogas production also reduces unpleasant odours in agriculture in the vicinity of populated areas. Moreover, the residual biomass possesses improved fertiliser quality and can be redistributed to fields more accurately than untreated organic waste. Of course, efficient fertilising reduces agrochemical pollution of surface and ground waters (Schulz & Eder 2001). Biogas also has social benefits. Its production will generate alternative sources of income especially in the agricultural sector of poorer countries and for smaller local companies. This is of particular significance in remote or economically underdeveloped regions. Additionally, strengthening traditional agriculture has a socio-cultural dimension as typical cultural landscapes may be preserved, even if new plants are introduced and new products are harvested. The opportunity to switch from low-income agriculture to biogas production may convince small farmers to adhere to their business and by that preserve the identity of agricultural communities. Overall, biogas is a promising alternative for the future, because its resource base is widely available, and even single farms or small local cooperatives could start biogas plant operation. 1.1 Upcoming concepts for energy plants Technologies to produce bioenergy from plants, their byproducts and from manure are well established, but the crop plants under consideration have been specifically selected for decades to yield optimum nutrient content for food and feed, and hence produce high value protein, oil or carbohydrate. It is not sustainable and not cost-effective, to ferment and end-oxidize these plants at relatively low economic yield. Hence, producing bioenergy from food and forage crops must be seen critically. As long as our concepts for energy plants are based on high yield cereals and other quality livestock feed, the cost of the energy produced will remain far too high to become competitive. If Europe is to compete on a global scale, it needs novel plants to produce cheap biomass and green manure, but to leave our food base untouched. 197 Novel Energy Plants The most abundant source of bioenergy is where most of the fixed carbon is deposited – the cell wall. New technologies have to be developed to modify cell wall composition to create a 'feedstock' that is more readily converted into fuels. Research on the production of novel energy plants requires (a) identification of plant species or mutants producing biomass with the optimum composition for the bioenergy market, e.g. biogas, (b) testing the agronomic capabilities of the chosen species, (c) studying how to produce bioenergy from the chosen species to exploit their potential, and (d) testing their performance on marginal or abandoned land in order to present sustainable and economically attractive alternatives to stake-holders. Only if these conditions are met, bioenergy plants will succeed, biotechnology will be strengthened, and we will successfully contribute to solve the world's energy problem. 1.2 Production base for energy plants Growing plants for biofuel production on the same, already limited available agricultural areas, will potentially increase food and fodder prices. This will be more pronounced in the poorer countries and less developed agricultural regions, which will leave them with even fewer chances to develop sustainable production systems. This is especially true in the Mediterranean where agricultural food production is strongly limited by water availability and soil quality. The lack of financial resources on farms in these countries leads to neglecting the production base and the soil, which ultimately increases soil degradation. As a result, such areas usually become abandoned and set aside – they are in fact withdrawn from the food production. It turns out that the present development is at the verge of becoming non-sustainable, similar to our previous behaviour in other economic areas. Taking all of the above into account, the only way out of this dilemma is to identify promising species and breed novel plants suitable to produce readily digestible carbohydrate, protein and oil, to be finally cropped on abandoned marginal and degraded agricultural land or so far unexploited soils, to enhance their capacity to build up biomass, and Fig. 1: View of an agricultural region of northern Greece. Different soil colours depict fertile and infertile areas. Abandoned land with eroded and low organic matter soil is more obvious around the area closest to the photographer 198 Subject Area 5.2 provide them with resistance against pests. When farmers start growing novel energy plants in crop rotation with local plants and leguminous species, they will enlarge the local production base (Fig. 1). Therefore, fast breeding methods must be employed to further develop these novel plants with traits essential for the bioenergy industry. These cultures of novel plants will require novel plant protection measures as well as crop rotation protocols to ensure sustainable productivity. After harvest, the biomass will feed local biogas production in the dry fermentation process. The electricity system of the local community will be stabilized at low cost, and the process heat can be used in households. Consequently, digested solid residues will be used to ameliorate the land and improve the soil quality. Such knowledge-based biotechnologies will provide farming communities with opportunities to increase energy and food availability, reduce energy costs and increase quality of life, conserve fossil fuel reserves, fight climate change and create new economic opportunities for small farms. 1.3 Plant breeding options Selection of desirable traits from conventional Mendelian breeding under field conditions takes several years and many plant generations to accomplish the goal. Conventional mutagenesis and in vitro selection can considerably shorten breeding times and complement field selection. With a view to legal and societal restrictions, conventional breeding (such as mutagenesis or in vitro breeding) could be a promising alternative to genetic transformation for the improvement of yield and other traits of high yielding crops. Those classical non-GM techniques are free from safety regulations in the EU Member States, and will allow one to screen & develop mutants under greenhouse and field conditions. Mutagenesis – Mutation techniques have often been used to improve yield, oil quality, disease, salt and pest resistance in crops, or to increase the attractiveness of ornamental plants. In some economically important crops (e.g. barley, durum wheat and cotton) mutant varieties nowadays occupy the majority of cultivated areas in many countries (Maluszynski et al. 1995). Mutagenesis has also played an important role in improving agronomic characteristics of Helianthus annuus L., one of the most important oil seed crops in the world. Osorio et al. (1995) have reported an increased variability in the oil fatty acid composition of sunflower mutants, obtained from seeds mutagenised with ethylmethanesulphonate (EMS). New sunflower mutants with enhanced biomass production and oil content were obtained by Chandrappa (1982) after mutagenesis with EMS or diethyl sulphate (DES). Kübler (1984) has obtained sunflower mutants of M2 and M3 generations with high linoleic acid content for diet food and mutants with high oleic acid content for special purposes like frying oils after EMS mutagenesis. Nehnevajova et al. (2007) used chemical mutagenesis to improve yield and metal uptake of sunflowers. In the second mutant generation sunflowers were obtained with improved yield (6–9 x), metal accumulation (2–3 x) and metal extraction efficiency (Cd 7.5 x, Zn 9.2 x; Pb 8.2 x) on a sewage sludge contaminated field. Whereas the best sun- Env Sci Pollut Res 15 (3) 2008 Subject Area 5.2 Novel Energy Plants Fig. 2: Chemical mutagenesis with ethyl metane sulfonate (EMS) as a promising approach for the production of novel plant varieties. EMS alters bases of the DNA by alkylating individual segments which leads to mispairings flower mutant could produce 26 t of dry matter yield per ha, control sunflower inbred lines produced only 3 t dry matter per ha and year in the same experimental site. These results demonstrate that EMS mutagenesis can lead to enhanced biomass production and partially to improved metal accumulation in sunflowers (Fig. 2). Moreover, classical mutagenesis has also been used to get new mutant variants with reduced metal accumulation traits. Nawrot et al. (2001) have obtained barley mutants with an increased level of tolerance to Al toxicity. Ma et al. (2002) have shown a rice mutant defective in Si uptake and Navarro et al. (1999) have isolated mutants of Arabidopsis thaliana, cdht 1 and cdht4, which accumulated 2.3 times less Cd than control plants exposed to 150 µM CdCl2. Mutation breeding has a long history with cotton where newly developed genotypes occupy significant cultivated area in several countries (Maluszynski et al. 1995). Initially, the efforts were concentrated towards improving either fibre quality or the pest resistance of the crop. With the more and more widespread use of cotton oil for dietary purposes, interest has increased in modifying its fatty acid composition (Abo-Hegazi et al. 1991, Bhat and Dani 1993). However, Env Sci Pollut Res 15 (3) 2008 no attempts have yet been made to improve the energetic value of the plant with the view of biofuel production. Attempts to characterize cotton biomass for energy production were so far mainly targeted towards biomass burning (Liao et al. 2004) or for biodiesel production through catalytic pyrolysis (Putun et al. 2006). Mutation breeding will therefore add yet another option to the possible uses of the crop, making its cultivation profitable on poor, degraded and/or polluted soils. This will be supported by the growing interest in cultivating energy crops in southern Europe, where the expansion in the last decade was aimed mainly towards low-input cropping systems. The development of new cotton mutants, better adapted for biogas production under low-input cropping systems, could provide a new pathway in the use of this traditional crop besides its much more obvious but much more resource-hungry use for fibre production. In vitro breeding (somaclonal variation – spontaneous mutations). Plant biotechnology involving modern tissue culture, using somaclonal variation and in vitro selection, offers the opportunity to develop new germplasm, better adapted to enduser demands (Alibert et al. 1994). Somaclonal variation can result in a range of genetically stable variations similar to 199 Novel Energy Plants variations induced with chemical mutagens (Skirvin et al. 1993, Jain et al. 1998). Somaclonal variation and in vitro selection seem to be also appropriate to develop plant variants with enhanced survival under adverse conditions (Herzig et al. 1997, Guadagnini et al. 1999, Nehnevajova et al. 2006). Fast breeding using molecular markers. Molecular markers are capable of providing efficient means for streamlining and speeding the breeding process. However, such markers have never been used for selecting of traits related to biogas production. An attempt to identify such markers in a model plant, well adapted to the conditions of South-Eastern Europe, will be of paramount importance. Cotton combines several essential characteristics for such kind of work: 1. irradiation mutagenesis is well documented to induce large numbers of genetic modifications in a single treatment in this crop, thus increasing chances that traits related to improved biogas production will be affected; 2. the identification of the most appropriate techniques and tools has already been a major subject of research (Bojinov and Lacape 2003, Lacape et al. 2003) and 3. the identification of DNAbased markers, linked to improved biomass characteristics for biogas production, bears the potential to tremendously facilitate future breeding programmes, aiming at developing specialized varieties. 2 Helping Plants to Do the Job 2.1 Identification of stress tolerance of both existing crops and newly bred genotypes The molecular and biochemical mechanisms of plant adaptation to stress conditions are still poorly understood and signalling pathways involved remain unclear (Dat et al. 2000, Schröder 2001). However, adaptation to environmental changes is crucial for plant growth and survival. When growing energy plants on marginal land in low-input systems, they may suffer from various stresses such as drought, heat, pathogens, nutrient deficiency or metal toxicity. Hence, currently cultivated crops, bred for productivity in high input cropping systems will prove unsuitable on poor and abandoned soils. In recent years, reactive oxygen species (ROS) have been suggested to act as intermediate signalling molecules to regulate gene expression (Mittler 2002, Mittler et al. 2004, Messner and Schröder 1999, Schröder et al. 2001, 2002). In this function, ROS have been proposed as a central component of plant adaptation to both biotic and abiotic stresses (Dat et al. 2000). These ROS are partially reduced forms of atmospheric oxygen (3O2) and can be very toxic since they attack several cell constituents such as proteins, lipids, or nucleic acids (Foyer and Noctor 2005). Many stresses, including drought, heavy metals, salt stress, heat shock or pathogen attack enhance the production of ROS (Mittler 2002). The use of ROS as signalling molecules suggests that during the course of evolution plants were able to achieve a high degree of control over ROS levels. The steady state level of ROS in the different cellular compartments is therefore controlled by an interplay between different ROS-producing and ROS-scavenging mechanisms (including enzymatic and non-enzymatic reactions). Oxidative stress and oxidative damage occur when both types of mechanisms are strongly imbalanced in the plant. 200 Subject Area 5.2 Several studies have demonstrated effects of oxidative, stressrelated responses (e.g. ROS-scavenging enzymes such as SOD, APOD, CAT, GST, GPOD, enzymes of ascorbate-glutathione pathway,….) and on other stress or housekeeping proteins (e.g dehydrin, actin, histone) in sunflower or tobacco exposed to drought, heat shock or metals at the metabolomic level (Bueno et al. 2002, Gallego et al. 1996, Zhang and Kirkham 1996), as well as at the transcriptomic level (Kiani et al. 2007, Rizhsky et al. 2002). It is clear that oxidative, stressrelated responses will influence plant performance and eventually lead to an accumulation of unwanted phenolic metabolites in the plant material. Hence, differences in stress resistance of various plant genotypes have to be evaluated with specific emphasis on the differences between parental genotypes and mutants, after exposure to increasing stress levels (drought, heat shock and/or metals). 2.2 Promoting plant growth by rhizosphere processes The plant genome is often considered to completely regulate plant productivity and stress resistance. However, mutualistic micro-organisms have the potential to affect plant productivity and even stress resistance. N2-fixing rhizobia live in association with the roots in specialized structures (nodules) and provide nitrogen to their host. Hence, leguminous cultures can help to enrich the poor soil with nitrogen, a property which makes these crops very suitable to take part in the rotation schemes of energy crops on marginal lands. The potentially beneficial effects of plant-microbe interactions on plant growth and tolerance are well documented (Hall 2002, Herrera et al. 1993, Mastretta et al. 2006). Mycorrhiza, as well as plant associated bacteria (rhizosphere or endophytic), can contribute to the nutrient supply of their plant hosts, which is important for optimal plant growth in normal conditions, but also for improving plant survival in hostile environments (Requena et al. 1997). Previous research with tobacco has already demonstrated growth increases, after inoculation with selected bacterial strains. Exploitation of the possibilities of microbial associations therefore opens new perspectives for the improvement of yield and the increase of stress tolerance of energy crops grown on marginal land. Endophytic bacteria have previously been isolated from tobacco plants and seeds grown on metal contaminated soil in Northern Europe (Mastretta et al. 2006). Reinoculation experiments showed that positive effects on growth were observed in (sterile) plants with seed endophytes, while endophytes isolated form whole plants on the contrary caused growth reductions. Mechanisms by which endophytic bacteria can promote plant growth include, e.g. biological nitrogen fixation, synthesis of phytohormones, or more particular properties such as metal tolerance or xenobiotic degradation pathways (Lodewyckx et al. 2001, Mastretta et al. 2006, Barac et al. 2004). An exploitation of such microbial associations opens perspectives for yield improvement and increases stress tolerance of energy crops grown on marginal land. Characterizing novel plants in this way will allow not only to draw conclusions about the genotypes under investigation, but also to gain more insight in the regulation and sequence of events occurring in plants in response to environmental changes. Env Sci Pollut Res 15 (3) 2008 Subject Area 5.2 2.3 Best practice in agronomy Monocultures of bioenergy crops are particularly vulnerable when cultivated on infertile soils and potential exposure to drought stress, pest and/or pathogen attacks. All forms of agriculture cause changes in the balances and fluxes of preexisting ecosystems, thereby limiting resiliency functions. The intensive agriculture in some regions, with its strong reduction of landscape structures and vast decoupling of energy and matter cycles, has caused stress and degradation of the production base; massive influence has also been exerted on neighbouring compartments. To overcome the economic, social and political inadequacies leading to ecological degradation during energy plant production, it is of paramount importance to transpose available knowledge on sustainable production systems, including remote sensing technologies, into knowledge-based practical instructions and political regulations on a regional scale. Thus, applied research for a sustainable and ecologically compatible land use is ever so important (Schröder et al. 2004). Studies with remote sensing have demonstrated the relationship between canopy spectral reflectance and biomass production of some major crops (Pinter et al. 2003). Reflectance data are typically derived from aircraft or satellite images in the visible and NIR ranges of the spectrum and subsequently transformed into vegetation indices (i.e. NDVI). However, the availability of this information by airborne platforms is constrained by weather conditions, revisit frequency and elaborate data processing. On the other hand, proximal sensors are an emerging technology designed to overcome the limitations of current instrumentation by delivering real-time data of high spatial resolution that can be used in site-specific management. Proximal sensors were recently used successfully for the prediction of biomass in irrigated corn, cotton and vineyards (Bausch and Delgado 2003, Stamatiadis et al. 2004, 2006). The application of this technology is expected to provide valuable management tools for increasing biomass production of energy crops. Plant stress tolerance under field conditions may also be successfully evaluated using photosynthetic parameters, such as leaf gas exchange and chlorophyll fluorescence. Their changes through stress development give a very good estimate about tolerance capacity. As non-destructive measures, these parameters have the advantage to provide reliable and fast information about plant behaviour at complex stress conditions. This was demonstrated in a screening study with cotton genotypes from different species grown under rain fed conditions in Bulgaria (Bojinov et al. 2000). Agricultural production systems have to be chosen that diminish soil and fertility losses, ensure water availability and fight pathogens. Farm practices that prevent erosion will help to protect soils and water quality. Sustainable agriculture will be achieved only when information about heterogeneity of soil-plant systems is available and appropriate plans are developed and implemented at the level of the local farm and the region. In order to make the production of novel energy plants possible, it is of utmost importance to develop adequate management systems. These should lower production costs, reduce pollution of surface and ground- Env Sci Pollut Res 15 (3) 2008 Novel Energy Plants water, reduce pesticide residues in food, reduce a farmer's overall risk, and increase both short- and long-term farm profitability (Parr et al. 1990). One important trait of mutants intended for low-input systems of South-Eastern Europe is their stress resistance to water shortage. Water stress will not only induce stomatal closure and limit photosynthetic activity, but also limit mineral N uptake and crop growth. The interaction between water availability and nutrient uptake is a crucial element that needs to be taken into account when testing the ability of new mutants to adapt to water-deficient environments. This can be achieved in site of specific field plot experiments that combine different irrigation and fertilization rates in a split-plot experimental design to yield best practise recommendations for a given region. The natural abundance of the stable isotopes of carbon (δ13C) and nitrogen (δ15N) in plant tissues has been used as integrated indicators of water stress and N nutrition, respectively. In the case of 13C, the isotopic signal has been generally used to identify differences in water stress over large topographic gradients or between mutants. For estimation of productivity potentials (Laitha and Marshall 1994), in the case of δ15N, the isotopic signal has been used to identify N uptake of the source fertilizer. Recent evidence indicates that the combined isotopic signal in the leaves is sensitive enough to identify water- or nutrient-stressed plants over short distances within single fields. This finding is significant when considering that conventional analytical methods may be unable to detect such small spatial differences in plant stress or nutrient deficiencies. This novel approach of interpreting isotopic data will be an important tool to explore biomass variation in the cultivation of energy plants. 3 Producing Biogas With fossil-based fuel prices steadily rising as the resources diminish, bioenergy will grow steadily and is fast becoming an energy industry factor, currently accounting for around 3% of US energy production. By 2030 it should have reached more than 10% in Europe. Moreover, as the EU and other countries stimulate research on energy production by legislation and corresponding incentives supporting Green Energy, investments into biogas production will become safe ground for agricultural communities. Modern dry fermentation has processing and technical advantages over the liquid fermentation process currently used for producing biogas. 3.1 Reactor types and research needs State-of-the-art digestion systems for energy crops are socalled aqueous digesters, i.e. energy crops are shredded and fed into digesters with a large amount of additional water leading to a concentration of usually below 5% dry substance in the reactor. This leads to large volumes of the digestion vessels since the residence time needs to be held at approx. 40 days in order to fully convert the digestible organic matter. The reactor type is – according to text books – an agitated vessel and thus operates always at a minimum concentration of organic matter. 201 Novel Energy Plants Subject Area 5.2 Markert 2006, Fränzle and Markert 2007]), which might lower gas production rates as compared to the conventional industrial environment. Hence, it is crucial to scrutinize the digestion process for the new plants, because if digestion is deteriorated by unexpected metabolites, they may not be useful, although they seemed promising at first glance. 4 Fig. 3: Flow chart of the biogas production process in a dry fermentation reactor Newer technology – so called dry digestion, does not dilute organic matter with water but keeps the organic matter unmixed with already digested matter and, thus, keeps the organics concentration always as high as possible. Using such a plug flow type reactor results in lower volumes due to the much higher concentration of organics, which range from approx. 35% to 12% between the feeding stage and the final stage of the process. An intercomparison shows that the plug flow type is very successful for organic waste application because of its rigidness against inhibition and side reactions. These benefits are combined with the shorter residence time of the reactor to boost its economic value. However, only little experience is available with running this reactor type on energy crops (Fig. 3). The energetic quality of the biogas depends on the fermentation process and on the characteristics of the actual substrate fed into the reactor. The challenge of optimal biogas production is to maintain a stable anaerobic digestion process and the technical solutions to achieve that are limited. Instead, it requires good quality energy plant material, accuracy, perseverance and experience on the side of the plant operators. The above hindrances are further complicated by the lacking technical protocols tackling these problems. The basic substrate for biogas production should be organic substances derived from plant matter, although other organic wastes might be added to the reactor. Residues of vegetable or animal fat are of particular interest in this respect, as they have high calorific values and thus enable high biogas yields. This co-digestion might also be beneficial for stabilising the fermentation process. It is known that inhibiting reactions may be caused by side products of the reactions or by ingredients originating from the crops. Mono digestions are particularly difficult due to the lack of trace minerals and – during dry digestion – the possibility of high salt concentration leading to high osmotic pressures, which might kill or seriously damage them. Using new energy crops may therefore lead to unexpected problems in the process (e.g. unexpectedly high heavy metal concentrations that could not be predicted by numerical approaches [Mohammed and 202 Conclusions In the European Union, biomass is regarded the most promising renewable energy option for the closer future (European Commission 1997, Wellinger et al. 1991). Biogas in particular has received considerable attention as a renewable energy carrier with a huge potential for the European market. Being usually produced by anaerobic digestion of wet agricultural products (including manure), the most widespread use of biogas is seen in the decentralised generation of electricity and heat to cover local demand. Excess electricity can even feed into local electricity networks. Alternatively, biogas can be added to the natural gas grid for power generation or heating purposes, or as a vehicle fuel. So far, biogas potential has been exploited to various extents and in different ways in different countries and regions. In Austria, Germany and Switzerland numerous biogas plants have been established, and the United Kingdom, France, the Netherlands, Denmark, Sweden and Belgium are also starting to further this technology (Abraham et al. 2007). However, most southern European countries, and especially new EU member states have not adopted this promising way to improve local energy production. It is therefore necessary to evaluate the potential of abandoned soils in South-Eastern Europe to grow plants that produce sufficient biomass at low costs, as a sustainable energy supply to poorer regions. The importance of the matter is hardly taken into account in the 7th Framework Program of the EU: Although hightech solutions for growth of biomass are presently available all over Europe, their sustainability is usually not achieved, resilience to numerous parameters is questionable, and clearcut evidence is presented in EU papers that these technical solutions are too expensive for many communities. Besides scientific progress, it will be of high importance to strengthen the European Research Area (ERA) by international cooperation to achieve common and well-developed strategies that respond to global change issues of high public concern such as energy plant and biogas production. These strategies should be applicable in all member states, and not only to those with lower net income. Cost effectiveness, reliability, long-term sustainability, resilience and reasonable input of resources are key characteristics of biogas production. Breeding new plants by a fast-track-breeding approach based on mutagenesis, aiming at the development of new genotypes which are particularly adapted to marginal soils, and resistant to the extreme climatic conditions in southern Europe is one of the most promising alternatives to conventional breeding, and also to GMO approaches. The exploitation of plant-microbial interactions as an alternative/ complement to chemical fertilisers to improve yield of plants is well known in organic farming, and it should be applied in energy plant production, as well as in the evaluation of Env Sci Pollut Res 15 (3) 2008 Subject Area 5.2 stress resistance of new plants by metabolomic and transcriptomic analyses. Further, and to not fall back into the mistakes of the agricultural production in the 1970s and 1980s, it will be important to optimize rotation schemes and soil management practices for the specific condition met in a region (Wei and Zhou 2006), hand in hand with an optimisation of crop mixtures in bio-reactors for optimal energy production. 5 Perspectives Europe is one of the leading players in the advancement of technologies and related environmental applications. European remote sensing satellites cover all of the Earth's climatic zones, while European ground-based, air-based and ocean-based monitoring devices serve users by providing high quality observation data in areas as diverse as urban planning, adaptation to and mitigation of climate change, disaster reduction, disease control and humanitarian relief. We will have to focus our work on the exploration of the finite and irreproducible resources, that is the land and the soils, and on their sustainable exploitation for food and energy (Haber 2007). Research on bioenergy plants and fossil fuel reduction is one of the major aims for the next decade, and this cannot be achieved by small groups or single institutions. With view to the impact in our information society, it is necessary to include as many stakeholders and groupings as possible in successful developments. Through the European Union's exhaustive efforts to promote greater awareness of science in society, results emanating from its environmental research initiatives may also have knock-on effects on the day-to-day decisions made by industry, commerce and Europe's citizens – the ultimate goal being to find a sustainable balance. Especially teams that include scientists from associated countries or new member states will influence this development by working together and investigate burning topics, with the aim of producing new environmental tools and technologies to promote sustainable development. This will help to establish rules and regulations for biogas production in the EU core countries and in the countries that will enlarge the ERA, and they will raise interest for the technologies by improving public awareness of the green technology used to protect our most valuable resource, the climate. SME partners involved will especially result in an enlarged cooperation and technology transfer across Europe, thus confirming the role of Europe as a leader in the export of innovative and environmentally friendly environmental technologies at affordable costs and high efficiency worldwide. References Abo-Hegazi AMT, Shaheen AM (1991): Use of mutations to improve cotton plants as an oil and protein source without affecting the seed cotton yield. Joint FAO/IAEA Div Nuclear Tech in Food and Agriculture, Vienna 2, 183–187 Abraham ER, Ramachandran S, Ramalingam V (2007): Biogas: Can it be an important source of energy? Env Sci Pollut Res 14 (1) 67–71 Alibert G, Aslane-Chanabé C, Burrus M (1994): Sunflower tissue and cell cultures and their use in biotechnology. Plant Physiol Bioch 32 (1) 31–44 Env Sci Pollut Res 15 (3) 2008 Novel Energy Plants Barac T, Borremans B, Provoost A, Oeyen L, Colpaert JV, Vangronsveld J, Taghavi S, van der Lelie D (2004): Engineered endophytic bacteria improve phytoremediation of water-soluble volatile organic pollutants. Nature Biotech 22, 583–588 Bausch WC, Delgado JA (2003): Ground-based sensing of plant nitrogen status in irrigated corn to improve nitrogen management. In: VanToai T et al. (eds), Digital imaging and spectral techniques: applications to precision agriculture and crop physiology, ASA Spec Publ. 66. ASA, CSSA, SSSA, Madison, WI., pp 145–157 Bhat MG, Dani RG (1993): Improvement in productivity and oil content of cotton (Gossypium hirsutum L.) cultivars through induced polygenic mutations. J Cotton Res Develop 7 (1) 9–18 Bojinov B, Lacape JM (2003): Molecular markers for DNA-fingerprinting in cotton. Proceedings World Cotton Research Conference-3, 9–13 March, Cape Town, Republic of South Africa Bojinov B, Vassilev A, Dimitrova L (2000): Comparative studies on the photosynthetic activity of two cotton varieties – Chirpan 603 (G. hirsutum L.) and C-6037 (G. barbadense L.) under severe drought and temperature stress. Plant Sci. (Blg) XXXVII (7) 452–458 Bueno P, Piqueras A (2002): Effect of transition metals on stress, lipid peroxidation and antioxidant enzyme activities in tobacco cell cultures. Plant Growth Regulation 36 (2) 161–167 Chandrappa HM (1982): Mutagenesis in sunflower (Helianthus annuus L). Thesis Abstr. 8, 256–257. In: Schuster WH, (ed) Die Züchtung der Sonnenblumen (Helianthus annuus L.) Advances in Plant Breeding 14, suppl. to J Plant Breeding, Parey, Berlin and Hamburg, pp 155 Dat J, Vandenabeele S, Vranova E, Van Montagu M, Inze D, Van Breusegem F (2000): Dual action of the active oxygen species during plant stress response. Cell Mol Life Sci 57, 779–795 Drake W (1983): Biomass tobacco as animal feed & energy base. Cultivators Research Service, Tesuque, N.M. EREC 2006 – Position paper. European Renewable Energy Council <www.erec-renewables.org> Foyer CH, Noctor G (2005): Oxidant and antioxidant signalling in plants: a re-evaluation of the concept of oxidative stress in a physiological context. Plant Cell Environ 28, 1056–1071 Fränzle S, Markert B (2007): Metals in biomass. From the biological system of elements to reasons of fractionation and element use. Env Sci Pollut Res 14 (6) 404–413 Gallego SM, Benavides MP, Tomaro ML (1996): Effect of heavy metal ion excess on sunflower leaves: Evidence for involvement of oxidative stress. Plant Science 121 (2) 151–159 Gaugitsch H (2004): A differentiated assessment of the future of biotechnology. Env Sci Pollut Res 11 (3) 141–142 Haber W (2007): Energy, food, and land – The ecological traps of humankind. Env Sci Pollut Res 14 (6) 359–365 Hall JL (2002): Cellular mechanisms for heavy metal detoxification and tolerance. J Exp Bot 53, 1–11 Herrera MA, Slamanka CP, Barea JM (1993): Inoculation of woody legumes with selected arbuscular mycorrhizal fungi and rhizobia to recover desertified Mediterreanean ecosytems. Appl Env Microbiol 59, 129–133 Herzig R, Guadagnini M, Erisman KH, Müller-Schärer H (1997): Chancen der Phytoextraktion. Sanfte Bodendekontamination von Schwermetallen mit Hilfe biotechnisch verbesserter Akkumulatorpflanzen. TerraTech 2, 49–52 Jain SM (1998): Plant biotechnology and mutagenesis for sustainable crop improvement. In: Behl RK, Singh DK, Lodhi GP (eds), Crop improvement for stress tolerance, pp 218–232, CCSHAU, Hissar & MMB, New Delhi, India Kiani SP, Grieu P, Maury P (2007): Genetic variability for physiological traits under drought conditions and differential expression of water stress-associated genes in sunflower (Helianthus annuus L.). Theor Appl Genet 114 (2) 193–207 203 Novel Energy Plants Kübler I (1984): Veränderungen verschiedener Inhaltsstoffe in einzelnen Sonnenblumenfrüchten nach mutagener Behandlung in M2 und M3. Fette-Seifen-Anstrichmittel 2, 62–70 Lacape JM, Nguyen TB, Thibivilliers S, Bojinov B, Courtois B, Cantrell RG, Burr B, Hau B (2003): A combined RFLP-SSRAFLP map of tetraploid cotton based on a Gossypium hirsutum x Gossypium barbadense backcross population. Genome 46, 612–626 Laitha K, Marshal JD (1994): Sources of variation in the stable isotope composition of plants. In: Lahjta K, Michener RM (eds), Stable isotopes in ecology and environmental science, pp 1–21, Blackwell, Oxford Liao C, Wu C, Yanyongjie HH (2004): Chemical elemental characteristics of biomass fuels in China. Biomass and Bioenergy 27, 119–130 Lodewyckx C, Taghavi S, Mergeay M, Vangronsveld J, Clijsters H, van der Lelie D (2001): The effect of recombinant heavy metal resistant endophytic bacteria in heavy metal uptake by their host plant. Int J Phytorem 3, 173–187 Long RC (1984): Edible tobacco protein. Crops and Soils Magazine, pp 13–15 Ma JF, Tamai K, Ichii M, Wu GF (2002): A rice mutant defective in Si uptake. Plant Physiol 130, 2111–2117 Maluszynski M, Ahloowalia BS, Sigurbjörnsson B (1995): Application of in vivo and in vitro mutation techniques for crop improvement. Euphytica 85, 303–315 Markard J, Buhler J, Madlener R, Truffler B, Umbach-Daniel A (2004): Development and diffusion of anaerobic digestion plants in Switzerland and Austria – Interaction of local regional and national innovation strategies. In: Internat Energiewirtschaftstagung, TU Wien 'Energiesysteme der Zukunft' (IEWT 2005), 16.–18.02.2005, Vienna Mastretta C, Barac T, Vangronsveld J, Newman L, Taghavi S, van der Lelie D (2006) Endophytic bacteria and their potential application to improve the phytoremediation of contaminated environments. Biotechnology and Genetic Engineering 23, 175–207 Messner B, Schröder P (1999): Burst amplifying system in cell suspension cultures of spruce (Picea abies): Modulation of elicitor-induced release of hydrogen peroxide (oxidative burst) by ionophores and salicylic acid. Appl Bot 73, 6–10 Mittler R (2002): Oxidative stress, antioxidants and stress tolerance. Trends Plant Sci. 7, 405–410 Mittler R, Vanderauwera S, Gollery M, Van Breusegm F (2004): Reactive oxygen gene network of plants. TiPS 9, 490–498 Mohammed MH, Markert B (2006): Toxicity of heavy metals on Scenedesmus quadricauda (Turp.) de Brebisson in batch cultures. Env Sci Pollut Res 13, 98–104 Navarro S, Dziewatkoski M, Enyedi A (1999): Isolation of cadmium excluding mutants of Arabidopsis thaliana using a vertical mesh transfer system and ICP-MS. J Env Sci Health 34, 1797–1813 Nawrot M, Szarejko I, Maluszynski M (2001): Barley mutants with increased tolerance to aluminium toxicity. Euphytica 120, 345–356 Nehnevajova E, Herzig R, Erismann KH, Schwitzguébel JP (2007): In vitro breeding of Brassica juncea L. to enhance metal accumulation and extraction properties. Plant Cell Rep 26 (4) 429–437 Nehnevajova E, Herzig R, Federer G, Erismann KH, Schwitzguébel JP (2007): Chemical mutagenesis – An efficient technique to enhance metal accumulation and extraction in sunflowers. Int J Phytorem 9, 149–165 Osorio J, Fernández-Martínez J, Mancha M, Garcés R (1995): Mutant sunflowers with high concentration of saturated fatty acids in the oil. Crop Sci 35, 739–742 Parr JF, Rapendick RI, Yangberg IG, Meyer RE (1990): Sustainable Agriculture in the United States. In: Edwards CA, Lal R, 204 Subject Area 5.2 Madden P, Miller RH, House G (eds), Sustainable Agricultural Systems Pinter PJ, Hatfield JL, Schepers JS, Barnes EM, Moran MS, Daughtry CS, Upchurch DR (2003): Remote sensing for crop management. Photogrammetric Engineering and Remote Sensing 69 (6) 647–664 Putun E, Uzun BE, Putun AE (2006): Production of bio-fuels from cottonseed cake by catalytic pyrolysis under steam atmosphere. Biomass & Bioenergy 30, 592–598 Rabl A, Benoist A, Dron D, Peuportier B, Spadaro JV Zoughaib A (2007): How to Account for CO2 Emissions from Biomass in an LCA. Int J LCA 12 (5) 281 Requenam BN, Jimenez I, Toro M, Barea JM (1997): Interactions between plant-growth promoting rhizobacteria (PGPR), arbuscular mycorrhizal fungi and Rhizobium spp. In the rhizosphere of Anthyllis cyitisoides, a model legume for revegations in Mediterranean semi-arid ecosystems. New Phytol 136, 667–677 Rizhsky L, Liang H, Mittler R (2002): The combined effect of drought stress and heat shock on gene expression in tobacco. Plant Physiol 130, 1143–1151 Schröder P (2001): The role of glutathione and glutathione Stransferases in the adaptations of plants to xenobiotics. In: Grill D, Tausz M, DeKok LJ (eds), Significance of glutathione in plant adaptation to the environment. Handbook Series of Plant Ecophysiology. Kluwer Acad Publ, Boston, Dordrecht, London, pp 157–182 Schröder P, Fischer C, Debus R, Wenzel A (2002): Reaction of detoxification mechanisms in suspension cultured spruce cells (Picea abies L. Karst.) to heavy metals in pure mixture and in soil eluates. Env Sci Pollut Res 10 (4) 225–234 Schröder P, Huber B, Munch JC (2004): Making modern agriculture sustainable: FAM Research Network on Agroecosystems. J Soils Sediments 3 (4) 223–226 Schulz H, Eder B (2001): Biogas-Praxis. 2. Rev Staufen bei Freiburg, Ökobuch Skirvin RM, Norton M, McPheeters KD (1993): Somaclonal variation: Has it proved useful for plant improvement? Acta Hort 336, 333–340 Stamatiadis S, Christofides C, Tsadilas C, Samaras V, Schepers J (2006): Natural abundance of foliar 15N as an early indicator of nitrogen deficiency in fertilized cotton. J Plant Nutr 29, 113–125 Stamatiadis S, Taskos D, Tsadilas C, Christofides C, Tsadila E, Schepers JS (2006): Relation of ground-sensor canopy reflectance to biomass production and grape color in two Merlot vineyards. Am J Enol Vitic 57, 416–422 Stamatiadis S, Tsadilas C, Schepers JS (2004): Real time crop sensors. In: Stamatiadis et al. (eds), Remote sensing for agriculture and the environment. Peripheral Publications, Larissa, Greece, pp 128–135 Wei SH, Zhou QX (2006): Phytoremediation of cadmium-contaminated soils by Rorippa globosa using two-phase planting. Env Sci Pollut Res 13, 151–155 World Energy Outlook (2006): <www.IEA.org> Young AL (2004): The future of biotechnology in support of biobased industries – The US perspective. Env Sci Pollut Res (2) 71–72 Young AL (2003): Biotechnology for food, energy, and industrial products: New opportunities for bio-based products. Env Sci Pollut Res 10 (5) 273–276 Zhang J, Kirkham MB (1996): Antioxidant responses to drought in sunflower and sorghum seedlings. New Phytol 132 (3) 361–373 Received: June 15th, 2007 Accepted: March 1st, 2008 OnlineFirst: March 2nd, 2008 Env Sci Pollut Res 15 (3) 2008